The use of strong base ion-exchange resins saturated with polyhalide, notably tri- and pentaiodide counter ions has been heretofore known in the art of water disinfection. Bacterially contaminated water, when contacted with a suitably prepared such polyhalide resin for sufficient time, is thereby disinfected.
The disinfection is a result of direct contact with the resin, the residual halogen in solution being insufficient to alone provide disinfection. The resins are to varying extents, "demand type" disinfectants, killing on contact.
References in the prior art to such iodated resins include U.S. Pat. Nos. 3,817,860; 3,923,665; 4,187,183; 4,190,529; 4,238,477 and published articles in Applied Microbiology, vol. 20, pages 720-722 (1970); ibid., vol. 44, pages 1370-1373 (1982); Industrial & Engineering Chemistry, Prod. Res. Dev. vol 19, p. 256-258 and 259-263 (1980); and Water Technology, pages 26-33, October 1987, pages 14-18, February 1988 and pages 65-67 August 1990.
Prior to the above mentioned disclosures, the use of interhalogens absorbed on ion exchanger resins was limited by severe halogen leakage from said resins, as reprted in U.S. Pat. No. 3,316,173, rendering further treatment necessary to obtain potable water. The above disclosures thus represent a significant advance in the art.
Nonetheless, it was soon recognized that the release of halogen atoms as ions or free halogen remained a major drawback to the use of bactericidal resins in other than emergency situations. This problem is addressed directly in U.S. Pat. No. 4,420,590, wherein it is generally claimed that the addition of specific small amounts of bromide ions, partially replacing triiodide resins with interhalogen ions such as I.sub.2 Br.sup.-, significantly reduces the level of halogen release, which it is claimed, provides a more physiologically acceptable product. It has been found, however, that when using tap water at the upper range of total disolved solids allowed by regulatory agency regulations in most countries, (i.e. over 800 ppm TDS) the level of iodine in the effluent of resins made according to the teachings of U.S. Patent '590 is above the desirable level, as described below.
Use of free bromine (Br.sub.2) in the manufacturing process could increase the amount of inter-halogen moieties in the finished product. This would serve the dual role of reduced iodine elution and reducing production cost, which has been a significant factor in limiting the use of disinfecting resins. Bromine and its compounds are much less expensive than the corresponding iodide compounds. However, the additional cost and difficulty of handling elemental bromine make this impractical in application. The goal of the present invention is the in situ, generation of bromine, allowing practical use of bromide compounds to produce a resin with high disinfection power and low iodine elution and lower in cost than the materials known currently in the art.
Thus the prior art, while recognizing the existence of unacceptable elution of halogens in the heretofor known polyhalide disinfectant resins, does not reveal a solution to this problem, generally applicable over the range of acceptable and commonly found levels of total dissolved solids (TDS) in drinking water. It would be highly desirable to have such a resin, which could be used for extended periods by most sections of the population in areas succeptable to microbial contamination, and at a price lower than that currently possible.